Deterioration inhibitor for rubber



Patented July 7, 1931 warren STATES PATENT OFFICE ALBERT M. CLIFFORD; F AKRON, OHIO, ASSIGNOE TO THE GOODYEAR TIRE & RUIB BER COMPANY, 01 AKRON, OHIO, A CORPORATION OF OHIO DETERIORATION INHIBITOR FOR RUBBER No Drawing. Application filed May 29,

This invention relates to the manufacture of rubber andrubber-like compounds and it has particular relation to the manufacture of compounds of that character which are ex- 5 posed to the effects of light, heat and oxygen.

The object of the invention is to provide a rubber compound which ofiers particularly high resistance to the above indicated weathering agencies whereby to preserve the material and to extend the period of usefulness thereof. I

Heretofore, it has been observed that rubber and rubber-like materials such as balata or gutta percha upon exposure to light, air

or heat either alone or in combination, tended quickly to harden'and'lose their tensile strength and elasticity and thereby becomes unfit for further service. It has been proposed to overcome or to retard these effects by incorporating into the compounds certain organic materials termed antioxidants or age retarderswhich tended to prevent the action of the ordinary weathering agencies.

Numerous materials have been proposed for this purpose among which are diphenylamine, hydroquinone and certain reaction products'of aldehydes and aromatic amines such as aldol and alpha naphthylamine.

However, most of the substances heretofore proposed as antioxidants have been objectionable for various reasons. Some ofthem were so expensive as to be impracticable for I commercial use. Others were objectionable because of their tarry or pitchy nature which rendered it difficult successfully to handle them and incorporate them into rubber. Still others were'cha-racterized by strong and disagreeable or even poisonous odors which necessitated special precautions in the ven- (moiio derivative) 1930. SeriaiNo. 457,495.

tilation in the plants in which they were employed.

This invention involves the discovery that naphthyl substituted benzidine compounds, particularly mono naphthyl and di-naphthyl substituted benzidines were highly efficient as preservatives and greatly extendthe period of utility of the rubber materials in which they are employed. Naphthyl benzidine of either the alpha or beta forms, may readily be prepared by subjecting benzidine and the naphthol to a temperature of 280 to 300 C. in an autoclave for a period of 8 to 10 hours. The reaction product consists of two components, one being the mono substituted naphthylene and the other being the disubstituted material. The formulae of these mate rials are respectively as follows:

\ i iH-KIF i (disubstituted derivative) While only the beta. derivatives of benzidine have been indicated in the formula, it is of course to be understood that analogous methods maybe employed in the manufacture of the alpha substituted material for use as antioxidants. Also, it is possible to form mixed alpha and beta substituted compounds by employing suitable conditions for the reaction. The naphthyl benzidines may be obdine from the disubstituted material. The The results of these various tests are tabu mono substituted material is crystallized lated as follows:

from the xylene in comparatively pure form. The disubstituted benzidine is left as a residue from the extraction of the boiling xylene and has a melting point of 236 to 238 C.

The invention is not limited to the naphthyl substituted benzidines but also includes naphthyl substituted tolidines or even corresponding xylidines. However, the latter materials are less practicable from a commercial viewpoint because of the expense in Volved in their preparation.

The above described naphthyl substituted benzidines may be employed as antioxidants in most of the standard rubber compounds. However, the following are specific examples of such formulae in which they have been found by actual test to give excellent results. 7

Two sets of samples were prepared from each of these two types of stock. These samples were then subjected to vulcanization for varying periods of time. One set from each type of stock was subjected immediately to physical tests in order to ascertain the tensile strength and elasticity thereof prior to aging. The second set of samples was subjected to a period of artificial agingor accelerated aging which was equivalent to a number of years of natural aging. Those samples prepared in accordance with For- 7 mula A were subjected to what is termed a low temperature test in which the samples were placed in an oxygen bomb under pressure of 150 pounds. per square inch for a period of six days at a temperature of 150 C. The second set of samples were subjected to what is termed a high temperature test in which they were placed in a bomb filled with air under a pressure of 80 pounds per square inch and subjected to a temperature of 114 C. for a period of 7 hours. At the conclusion of these periods of artificial aging, the samples were removed from thebomb and subjected to physical tests corresponding to those conducted upon the unaged samples.

LOW TE MPERATURE TEST Stock A Cure Stress in kgs/cm at Elong. Per cent at weight Time in Temp. 500% 700% Ema], break increase mins. F elong. clong.

Mono beta naphthyl benzidine Original Aged 6 days in oxygen bomb s. Di-beta naphthyl benzidine Original Aged 6 days in oxygen bomb HIGH TEMPERATURE TEST Stock B i 'Mono beta naphthyl benzidine Original Aged '7 hours in air bomb s. Di-beia naphthyl benzidine Original Aged 7 hours in air bomb It will be apparent that those materials containing either the mono or dinaphthyl substituted benzidine resisted the attacks of oxygen and heat even under the comparatively severe conditions existing in the bomb and retained a large portion of their tensile strength and elasticity under conditions which would have reduced stocks containing no antioxidants to resinous masses substantially devoid of tensile strength and elasticity. As previously intimated, these new types of antioxidants, in addition to being highly effective as age retarders, are also comparatively inexpensive to manufacture and are neither odorous or toxic in nature. F or that reason, they may be employed in factories without any unusual or extensive precautions in order to overcome odors or to prevent undesirable physiological effects upon the workmen employed in handling them Although I have described but the preferred forms of the invention, it will be apparent to those skilled in the art that the in vention is not so limited but that various substituted benzidine.

3. A method of treating rubber which comprises subjecting it to vulcanization in the presence of a naphthyl substituted benzidine.

4. A method of preserving rubber which comprises subjecting it to vulcanization in the presence ofa dinaphthyl substituted benzidine.

5. A method of preserving rubber which comprises subjecting it to vulcanization in the presence of a material having the formula in which R and R are naphthyl radicals and R is a dephenyl nucleus.

6. A method of preserving rubber which comprises subjecting it to vulcanization in the presence of a material having the formula R1l TR2I IRa,

in which R, and R are naphthylene groups and R is a material selected from a group consisting of diphenyl and methyl substituted diphenyl.

7. A method of preserving rubber which comprises subjecting it to vulcanization in the presence of a naphthyl substituted mate- 7 rial selected from a class consisting of benzidine and methyl substituted benzidine.

8. A method of preserving rubber which comprises subjecting it to vulcanization in the presence of a material selected from a group consisting of di-beta naphthyl substituted benzidine and di-beta naphthyl substituted tolidine.

9. A method of preserving rubber which comprises subjecting it to vulcanization in the presence of di-beta naphthyl substituted benzidine.

10. A rubber product that has been vulcanized in the presence of a naphthyl substituted derivative of the benzidine group.

11. A method of preserving rubber which comprises subjecting it to vulcanization in the presence of a naphthyl substituted material selected fronr a class consisting of benzidine and methyl substituted benzidine.

12. A rubber product that has been vulcanized in the presence of a material having the formula in which R and R are naphthyl groups and R is a diphenyl radical.

In witness whereof, I have hereunto signed my name.

Signed at Akron, in the county of Summit and State of Ohio, U. S. A., this 28th day of May, 1930.

ALBERT M. CLIFFORD. 

